Process for coding and decoding stereophonic spectral values

Abstract

A method of coding stereo audio spectral values first carries out grouping of those values in scale factor bands, with which scale factors are associated. Sections are formed next, each comprising at least one scale factor band. The spectral values are coded within at least one section with a code book assigned to the section, out of a plurality of code books each with a code book number assigned to it, the number of the code book used being transmitted as side information to the coded stereo audio spectral values. At least one additional code book number is provided, which does not refer to a code book but shows information relevant to the section to which it is assigned. A method of decoding stereo audio spectral values which are partly coded by the intensity stereo process and which have side information uses the relevant information, showing the additional code book numbers, to cancel the existing coding of the stereo audio spectral values.

What is claimed is:  
     
       1. A method of coding stereo audio spectral values, comprising the steps of: 
       grouping the stereo audio spectral values in scale factor bands with which scale factors are associated;  
       forming sections, each comprising at least one scale factor band;  
       allocating a predetermined code book out of a plurality of predetermined code books to at least one section, to obtain an allocated predetermined code book for the at least one section wherein each of the predetermined code books has assigned to it a unique code book number;  
       coding the stereo audio spectral values within the at least one section using the allocated code book, to obtain coded stereo audio spectral values for the at least one section;  
       transmitting a unique code book number assigned to be allocated code book as side information for the coded stereo audio spectral values in the at least one section at a code book number position required by a bit stream syntax for a section;  
       allocating an additional code book number to another section, wherein the additional code book number is not assigned to a predetermined code book out of the plurality of predetermined code books, the additional code book number signaling to a decoder, encoding information relevant to the another section, the encoding information not including a reference to a predetermined code book out of the plurality of predetermined code books;  
       transmitting the additional code book number as side information for the another section at the code book number position required by the bit stream syntax for a section;  
       wherein either a unique code book number assigned to a predetermined code book out of the plurality of predetermined code books or the additional code book number signaling the encoding information is transmitted at the code book number position required by the bit stream syntax, so that an amount of side information for a section that is not affected by signaling the encoding information to the decoder.  
     
     
       2. A method of decoding a coded signal having at least one section of coded stereo audio spectral values and another section, each section having, as side information, a code book number position required by a bit stream syntax, comprising the steps of: 
       detecting a code book number for each section of the coded signal at the code book number position based on the bit stream syntax for obtaining, for the at least one section, a detected unique codebook number being assigned to a predetermined code book out of a plurality of predetermined code books and for obtaining, for the another section, a detected additional code book number, wherein the additional code book number is not assigned to a predetermined code book out of the plurality of predetermined code books, the additional code book number signaling, to a decoder, encoding information relevant to the another section, the encoding information not including a reference to a predetermined code book out of the plurality of predetermined code books;  
       decoding the stereo audio spectral values of the at least one section, using a predetermined code book out of the number of predetermined code books, the predetermined code book having assigned to it the detected unique code book number; and  
       decoding the another section using the encoding information signaled by the detected additional code book number.  
     
     
       3. The method according to  claim 1  or  2 , wherein a to be encoded signal includes a first section having spectral values of a first channel and a corresponding second section having spectral values of a second channel; 
       wherein the method further comprises the step of intensity stereo encoding the first and the second section to obtain intensity stereo encoded stereo audio spectrala values for the at least one section and a zero spectrum for the another section;  
       wherein the additional code book number is allocated to the another section, the additional code book number signaling to a decoder that the intensity stereo encoding has been performed for the first section and the second section.  
     
     
       4. The method according to  claim 1  or  2 , further comprises performing the step of adaptive Huffman encoding for stereo audio spectral values in the another section, the step of adaptive Huffman encoding including a step of producing an adapted Huffman code book based on signal statistics of the stereo audip spectral values in the another section and transmitting information on the adapted Huffman code book as additional side information for the another section; 
       wherein the additional code book number signals, to a decoder that adaptive Huffman encoding of the stereo audio spectral vaues of the another section has been performed.  
     
     
       5. The method according to  claim 3 , wherein the additional code book number also indicates, as encoding information, a phase relationship between the first section having spectral values of the first channel and the corresponding second section having spectral values of the second channel. 
     
     
       6. The method according to  claim 5 , wherein there exists, in addition to the additional code book number, another additional code book number, wherein one of the two additional code book numbers indicates as identical phase position of the first and second channels, and 
       wherein the one of the two additional code book numbers indicating an identical phase position of the first and second channels is allocated to the another section, when the first and second channels have an identifcal phase position, the encoding information signaled to a decoder indicating that the following calculating-back formula is to be applied for intensity decoding in the decoder:  
       
         
             R   i =0.5{circumflex over ( )}(0.25·is _pos( sfb ))· L   i ,  
         
       
        where R i  are the stereo audio spectral values of a second channel, is _pos represents intensity direction information for a scale factor band sfb, and L i  are the stereo audio spectral values of a first channel.  
     
     
       7. The method of according to  claim 5 , wherein there exists, in addition to the additional code book number, another additional code book number, wherein one of the two additional code book numbers indicates an opposing phase position of the first and second channels; and 
       wherein the one of the two additional code book numbers indicating an opposing phsase position of the first and second channels is allocated to the another section, when the first and second channels have an opposing phase position, the encoding information signaled to a decoder indicating that the following calculating-back formula is to be applied for intensity decoding in the decoder:  
       
         
             R   i =(−1)·0.5{circumflex over ( )}(0.25.·is_pos( sfb ))· L   i ,  
         
       
        where R i  are the stereo audio spectral values of a second channel, is _pos represents intensity direction information for the scale factor band sfb, and L i  are the stereo audip spectral values of a first channel.  
     
     
       8. The method according to  claim 3 , wherein the step of intensity stereo encoding forms a standardized sum signal of the stereo audio spectral values of the first channel and the second channel, in the at least one section, while in the another section a spectrum is zero, and intensity direction information is coded as side information. 
     
     
       9. The method according to  claim 1 , wherein a to be encoded signal includes a first section having spectral values of a first channel and a corresponding second section having spectral values of a second channel, further comprising the step of writing a bit mask which has a bit for each scale factor band; 
       wherein the step of writing includes setting or not setting a mask bit depending on a phase relationship of the first channel and the second channel and a valve of the additional code book number; and  
       wherein the additional code book number signals, as encoding information, to a decoder that the decoder is to gate a bit on the mask for a scale factor band is gated with the additional code book number in a section, to determine the phase relationship of the first channel and the second channel.  
     
     
       10. The method according to  claim 9 , wherein the bit mask is an MS bit mask, and the additional code book numbers is to be gated with the MS bit mask scale factor band wise by means of an EXCLUSIVE-OR gate. 
     
     
       11. The method according to  claim 2 , wherein the additional code book number allocated to the another section signals to a decoder that intensity stereo encoding has been performed for a to be encoded signal including a first section having spectral values of a first channel and a corresponding second section having spectral values of a second channel; and 
       wherein the step of decoding the another section includes the step of intensity stereo decoding using intensity stereo encoded spectral values obrained by the step of decoding the stereo audio spectral values of the at least one section and intensity encoding information from the another section to obtain intensity stereo decoded stereo audio spectral values for the first section and the second section.  
     
     
       12. The method according to  claim 2 , wherein, when generating the coded signal, the step of adaptive Huffman encoding for stereo audio spectral values in the another section has been performed, the step of adaptive Huffman encoding including producing an adapted Huffman code book based on signal statistics of the stereo audip spectral values in the another section and transmitting information on the adapted Huffman code book as additional side information for the another section, the method further comprising the following step: 
       when the additional code book number signals that adaptive Huffman encoding of the stereo audio spectral values of the another section has been performed, retrieving information on the adapted Huffman code book from the side information; and  
       wherein the step of decoding the another section includes the step of Huffman decoding using the adaptive Huffman code book.  
     
     
       13. The method according to  claim 11 , wherein the additional code book number indicates, as encoding information, a phase relationship between the first section having spectral values of the first channel and the corresponding second section having spectral values of the second channel. 
     
     
       14. The method according to  claim 13 , wherein there exists, in addition to the additional code book number, another additional code book number, wherein one of the two additional code book numbers indicates an indentical phase position of the first and second channels; 
       wherein the one of the two additional code book numbers indicating an identical phase position of the first and second channels is allocated to the another section, when the first and second channels have an identical phase position; and  
       wherein the step of decoding the additional section includes the step of applying the following calculating-back formula:  
       
         
             R   i =0.5{circumflex over ( )}(0.25·is pos( sfb ))· L   i    
         
       
        where R i  are the stereo audio spectral values of a second channel, is _pos represents intensity direction information for a scale factor band sfb and L i  are the stereo audio spectral values of a first channel.  
     
     
       15. The method according to  claim 13 , wherein there exists, in addition to the additional code book number, another additional code book number, wherein one of the two additional code book numbers indicates an opposing phase position of the first and second channels; 
       wherein the one of the two additional code book numbers indicating an opposing phase position of the first and second channels is allocated to the another section, when the first and second channels have an opposing phase position; and  
       wherein the step of decoding the additional section includes the step of applying the following calculating-back formula:  
       
         
             R   i =(−1)·0.5{circumflex over ( )}(0.25·is pos( sfb ))· L   i    
         
       
        where R i  are the stereo audio spectral values of a second channel, is _pos represents intensity direction information for the scale factor band sfb, and L i  are the stereo audio spectral values of a first channel.  
     
     
       16. The method according to  claim 11 , 
       wherein the step of intensity stereo encoding forms a standardized sum signal of the stereo audio spectral values of the first channel and the second channel, in the at least one section, while in the another section a spectrum is zero, and intensity direction information is coded as side information.  
     
     
       17. The method according to  claim 2 , wherein the coded signal is derived from a to be encoded signal, the to be encoded signal including a first section having spectral values of a first channel and a corresponding second section having spectral values of a second channel, the coded signal further comprising a bit mask which has a bit for each scale factor band, wherein a mask bit is set or not depending on a phase relationship of the first channel and the second channel and a value of the additional code book number; and 
       wherein the step of decoding the another section includes the step of gating a bit on the mask for a scale factor band with the additional code book number in a section, to determine the phase relationship of the first channel and the second channel.  
     
     
       18. The method according to  claim 17 , wherein the bit mask is an MS bit mask, and the additional code book number is gated with the MS bit mask scale factor band wise by means of a EXCLUSIVE-OR gate. 
     
     
       19. An apparatus for coding stereo audio spectral values, comprising: 
       a means for grouping the stereo audip spectral values in scale factor bands with which scale factors are associated;  
       a means for forming section, each comprising at least one scale factor bandL;  
       a means for allocating a predetermined code book out of a plurality of predetermined code books to at least one section, to obtain an allocated predetermined code book for the at least one section, wherein each of the predetermined code books has assigned to it a unique code book number;  
       a means for coding the stereo audio spectral values within the at least one section using the allocated code book, to obtain coded stereo audio spectral values for the at least one section;  
       a means for transmitting a unique code book number assigned to the allocated code book as side information for the coded stereo audio spectral values in the at least one section at a code book number position required .by a bit stream syntax for a section;  
       a means for allocating an additional code book number ot another section wherein the additional code book number is not assigned to a predetermined code book out of the plurality of predetermined code books, the additional code book number signaling to a decoder, encoding information relevant to the another section, the encoding information not including a reference to a predetermined code book out of the plurality of predetermined code books; and  
       a means for transmitting the additional code book number as side information for the another section at the code book number position required by the bit stream syntax for a section;  
       wherein either a unique code book number assigned to a predetermined code book out of the plurality of predetermined code books or the additional code book number signaling the encoding information is transmitted at the code book number position required by the bit stream syntax, so that an amount of side information for a section is not affected by signaling the encoding information to the decoder.  
     
     
       20. An apparatus for decoding a coded signal having at least one section of coded stereo audio spectral values and another section, each section having, as side information, a code book number position required by a bit stream syntax, comprising: 
       a means for detecting a code book number for each section of the coded signal at the code book number position based on the bit stream syntax;  
       a means for obtaining for the at least one section, a detected unique codebook number being assigned to a predetermined code book out of a plurality of predetermined code books;  
       a means for obtaining, for the another section, a detercted additional code book number, wherein the additional code book number is not assigned to a predetermined code book out of the plurality of predetermined code books, the additional code book number signaling, to a decoder, encoding information relevant to the another section, the encoding information not including a reference to a predetermined code book out of the plurality of predetermined code books;  
       a means for decoding the stereo audip spectral values of the at least one section using a predetermined code book out of the number of predetermined code books, the predetermined code book having assigned to it the detected unique code book number; and  
       a means for decoding the another section using the encoding information signaled by the detected additional code book number.